Box fan



FIG. 1 is a front elevational view of a box fan showing our new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is an enlarged top plan view thereof;

FIG. 4 is an enlarged right side elevational view thereof; and,

FIG. 5 is an enlarged left side elevational view thereof.

The ornamental design for a box fan, as shown.